Effect of λ/2 SiO_2 overcoat on the laser damage of HfO_2/SiO_2 high-reflector coatings

摘要

The effect of λ/2 SiO_2 overcoat on the laser damage characteristics of HfO_2/SiO_2 high-reflector (HR) coatings is investigated with 1-on-1 and N-on-1 laser damage test methods. The laser damage surface of 1-on-1 is analyzed by a step analyzer. The surface morphologies show that laser damage makes the coating damaged area protrudent and rough for HR coating without λ/2 silica overcoat, but concave and smooth for HR coating with A/2 silica overcoat. The result of 10-on-1 multi-pulse irradiation on the same point of the coating shows that there is an energy density stage on the damage curve. If the laser energy density is within the range of the stage, HfO_2/SiO_2 HR coatings with λ/2 silica overcoat will not be damaged more than 2 times for multi-shots, and the surface damages are very slight so that there is no impact on the coating performance. Another interesting result is that the energy density stage extends from the damage threshold to the point of about 3 times of threshold, which is similar to the effect of the laser condition on coating.